The present invention relates to internal combustion engines of the type in which the compression ratio and the swept volume may be altered during operation of the engine. More specifically, the invention relates to internal combustion engines including one or more pistons, each of which is mounted to reciprocate in a respective cylinder and is pivotally connected to a connecting rod which is connected to a respective crank on a crankshaft, the connecting rod being pivotally connected to one end of an elongate link member which is pivotably connected to the associated crank at a point intermediate its ends and whose other end constitutes a rod which is restrained by a mounting such that it may pivot about a pivotal axis parallel to the axis of the crankshaft, the mounting including a first movable mounting member and a second movable mounting member, the first movable mounting member being connected to the rod by a connection which permits only relative sliding movement in the direction of the length of the rod and the first movable mounting member being connected to the second movable mounting member to be pivotable with respect thereto about the said pivotal axis, a single actuating means being provided which cooperates with the second movable mounting member and is arranged to move it.
Such an engine is disclosed in EP-B-0898644. In the engine disclosed in this patent, the first mounting member comprises a sleeve or the like which slidably retains the rod of the link member and is pivotally connected to the second mounting member which is selectively movable by an actuator in a direction parallel to the axis of the associated cylinder. Movement of the first mounting member in this direction results primarily in a change in the top dead centre position of the piston and thus in the compression ratio, though also in a small change in the bottom dead centre position of the piston and thus in the stroke of the piston.
It is, however, often desirable to be able to make a substantial change to the stroke of the piston and thus to the swept volume of the engine and to this end EP-B-1012459 discloses a modified engine which includes two actuators. The first actuator is arranged to move the first mounting member parallel to the cylinder axis, and thus changes the compression ratio of the engine, and is carried by the second actuator, which is arranged to move the first actuator and thus the first mounting member perpendicular to the cylinder axis and thus changes the stroke of the piston and thus the swept volume of the engine. The engine of EP-B-1012459 thus enables the compression ratio and the swept volume of the engine to be changed at will independently of one another.
However, the inclusion of a second actuator in the engine of EP-B-1012459 adds not inconsiderably to its structural complexity and cost and also to the complexity of the control system that is required. Although the engine may be operated with any desired combination of values of compression ratio and swept volume within the ranges that may be obtained, it is now appreciated that this is in fact not necessary in all cases. Thus at relatively low speed and/or load a relatively small swept volume and a relatively high compression ratio are desirable whilst at relatively high speed and/or load a relatively large swept volume and a relatively low compression are desirable. Although the actuators are able to position the mounting so that a large swept volume is provided in combination with a high compression ratio and also a small swept volume in combination with a low compression ratio, these operating configurations may in practice rarely be required.
It is in practice necessary, in connection with the engines disclosed in the prior patents referred to above, to provide an extension to the crankcase which constitutes a housing for the actuator system beside the engine roughly at the level of the crankshaft. In practice, some vehicle engine compartments and space constraints may render the provision of such a structure difficult.